The invention relates to a microphone used in a video camera etc.
There has conventionally been available such a directional microphone used in a video camera etc. as follows. That is, this microphone includes a capacitor microphone unit and an amplification circuit board housed and disposed in a cylindrical housing having a structure enhancing directivity and also houses and disposes this cylindrical housing in an outer cylinder. Between the cylindrical housing and the capacitor microphone unit is sandwiched vibration preventing rubber. Likewise, between the cylindrical housing and the outer cylinder is also disposed vibration preventing rubber. In such a configuration, an audio signal converted into an electric signal by the capacitor microphone unit is amplified by the amplification circuit board and then issued to the outside. It should be noted that the cylindrical housing houses a battery therein in some cases.
This prior art microphone, however, suffers from a problem of occurrence of an interference sound caused by an electromagnetic wave. The interference sound here refers to the following. That is, it refers to a noise sound superimposed on a recorded speech sound which occurs due to a high-frequency component contained in an external electromagnetic wave when the speech sound is recorded by a microphone.
With recent prevalence of portable telephones, there have been increasing such cases that many unspecified persons including reporters using a microphone use those portable telephones in communication at a recording site requiring a microphone. In particular, if a reporter uses his portable telephone while recording a variety of speech sounds, he would use his microphone and portable telephone in such a state where they are very close to each other. Such a use situation of a microphone may occur on an every-day basis in the future too when a news site is reported using a video camera etc. having a built-in microphone.
Although an influence of an electric field generated by a portable telephone reaches relatively short, it is known that in its vicinity (within a few to few tens of centimeters therefrom), that field has a very high strength of a few tens of volts/meter, which is a few tens of thousands of times as much as that generated over the cities by a commercial radio wave.
If a microphone and a portable telephone are used as being very close to each other, an electromagnetic wave generated by the portable telephone has a remarkable influence on the microphone, so that an interference sound is mixed into an audio signal. This is described specifically as follows.
A microphone can be considered to be an operation circuit of an FET transistor the gate of which serves as a diaphragm of a capacitor microphone unit. In the operation circuit of such an FET transistor, a vibration generated by a sound pressure of speech sound is captured as a potential induced across an electret film which constitutes the diaphragm. Accordingly, in the microphone, a sound-pressure deviation is captured as a voltage deviation, which is in turn taken in as a change in voltage input to the gate of the FET transistor. The change in voltage input thus taken in is used as an audio signal input to thereby operate the microphone.
If a high-frequency strong electric field occurs near a microphone unit having such characteristics, a nonlinear distortion occurs in an input/output circuit or other electric circuits of the electret film or FET transistors, so that an envelope detected-wave output of a frequency-modulated, amplitude-modulated, and digital-modulated high-frequency signals appears in an audio band. Further, a similar detected-wave output appears also at a subsequent-stage amplification circuit board. Such a detected-wave output gives rise to various high-frequency interference sounds in the audio signal.
The recent prevalence of portable telephones has been shifting a service frequency band toward a higher frequency side (e.g., 1.5 GHz), so that presently an influence of electromagnetic waves on such a microphone is becoming more and more remarkable. Accordingly, there is desired such a microphone that is not easily influenced by electromagnetic waves.
Also, to prevent beforehand any disturbance due to malfunction etc. of a variety of electronic apparatuses caused by an electromagnetic wave, many counties have laws ahd regulations of the electrbmagnetic-wave resistance of such electronic equipment. One example is CE (Conformite Eoropeenne) in Europe. Further, with prevalence of high-electromagnetic-wave generators used by individuals represented by a portable telephone, many countries are trying to prevent beforehand the future-expected disturbance caused by an electromagnetic wave by further tightening those laws and regulations so that only such products that have a higher electromagnetic-wave resistance may be allowed to circulate in the world markets. In view of such a status quo, the microphone is also desired to have an even higher electromagnetic-wave resistance.
To solve the above-mentioned problems, the prior-art microphone is also provided with a grounding path for connecting a grounding part thereof to the ground. This grounding path, however, is comprised of a lead wire for interconnecting the microphone unit and the amplification circuit board, a grounding wiring line in the amplification circuit board, and a lead wire for interconnecting the amplification circuit board and a microphone cable, so that it cannot be the shortest path effective enough to remove an interference sound caused by a high-frequency electric field.
A In view of the above, it is an object of the invention to provide a microphone unit which can effectively remove an interference sound caused by a high-frequency electric field.
A microphone or a video camera according to the invention includes a microphone unit, a cylindrical housing made of a conductor for housing the microphone unit, and an intermediate connector which electrically connects a grounding part of the microphone unit to the cylindrical housing along essentially the shortest path while blocking mechanical vibrations. In this configuration, it operates as follows.
Even if an electric field induced by an electromagnetic wave present around the microphone is formed in the cylindrical housing to correspondingly cause such a high-frequency signal to occur in the microphone unit that contains a modified signal which gives an interference sound to the microphone, the high-frequency signal is led through the intermediate connector to the cylindrical housing along essentially the shortest distance. By grounding the cylindrical housing beforehand, therefore, such a high-frequency signal occurring at the microphone unit can be securely discharged to the ground through the cylindrical housing. Moreover, the cylindrical housing, which is a conductor having a simple construction and also which has a vibration preventing mechanism between itself and an outer cylinder, serves to connect the microphone unit to the ground potential therethrough along essentially the shortest path not longer than necessary. This configuration enables to securely decrease the interference sound caused by such a high-frequency signal as mentioned above.
It should be noted that the cylindrical housing has a simple construction and so is liable to be exposed to the outside at part of a peripheral surface or end thereof, so that it can be grounded relatively easily.
Also, in the improved microphone of the invention, the intermediate connector is made of an elastic short-hair-shaped conducting member, which itself is protruded from either one of the microphone unit and the cylindrical housing as having its tip abutted against the other. In this configuration, the following is possible.
The short-hair-shaped conducting member can give a sufficient function required on the intermediate connector of electrically interconnecting the two while blocking the mechanical vibrations and also can be mounted relatively simply.
Also, in the improved microphone of the invention, the intermediate connector is made of an elongated conducting slice which is twist-reformed. This has the following effects.
The twist-reformed elongated conducting slice can give a sufficient function required on the intermediate connector of electrically interconnecting the two while blocking the mechanical vibrations and also can be mounted relatively easily.
Also, in the improved microphone of the invention, the amplification circuit board for amplifying an output signal of the microphone unit is housed in the cylindrical housing and also has its grounding part electrically connected to the cylindrical housing along essentially the shortest distance. This has the following effects.
It is possible to discharge through the cylindrical housing to the ground such a high-frequency signal which may possibly occur, due to an electromagnetic wave present around the microphone, in the amplification circuit board that contains a modified signal which may give an interference sound to the microphone.
Also, the improved microphone of the invention further includes a lid made of a conductor which seals the end of the cylindrical housing and also electrically connected thereto and a microphone cable which passes through the lid from the inside to the outside of the cylindrical housing for providing an output signal of the microphone to the outside in such a configuration that a shield layer of the microphone cable is electrically connected to the lid. This has the following effects.
The cylindrical housing can be electrically connected through the lid to the shield layer of the microphone cable, thus connecting the cylindrical housing to the ground potential easily and along the shortest distance.
Also, the improved microphone of the invention further includes an outer cylinder made of a conductor for surrounding the peripheral surface of the cylindrical housing and another intermediate connector for electrically interconnecting the cylindrical housing and the outer cylinder with essentially the shortest distance while blocking the mechanical vibrations. This has the following effects.
If an electric field is formed, due to an electromagnetic wave present around the microphone, at a gap between the cylindrical housing and the outer cylinder, such a high-frequency signal corresponding to the electric field may occur on the microphone unit, the cylindrical housing or the outer cylinder that contains. a modulated signal giving an interference sound to the microphone. Thus generated high-frequency signal, however, passes through the former intermediate connector and the another intermediate connector to the cylindrical housing or the outer cylinder. Accordingly, by connecting the cylindrical housing or the outer cylinder to the ground potential, the high-frequency signal can be securely decreased through the cylindrical housing or the outer cylinder to the ground potential. Moreover, the cylindrical housing or the outer cylinder, which is made of a conductor having a simple construction, is used to ground the microphone therethrough, thus enabling essentially minimizing a path in length not longer than necessary between the microphone unit and the ground potential. This also contributes to mitigating of the high-frequency signal. Also, the outer cylinder, like the cylindrical housing, is simple in construction and has often part of the peripheral surface thereof exposed to the outside, thus enabling connecting the outer cylinder to the ground potential relatively easily.
Also, in the improved microphone of the invention, the another intermediate connector is made of an elastic short-hair-shaped conducting member, which is protruded from either one of the cylindrical housing and the outer cylinder as having its tip as abutted against the other. This has the following effects.
The short-hair-shaped conducting member can sufficiently have a function required on the another intermediate connector of electrically interconnecting the two with essentially the shortest distance while blocking the mechanical vibrations and also can be mounted relatively easily.
Also, in the improved microphone of the invention, the another intermediate connector is made of a twist-reformed elongated conducting slice. This has the following effects.
This twist-reformed elongated conducting slice can sufficiently have a function required on the another intermediate connector of electrically interconnecting the two while blocking the mechanical vibrations and also can be mounted relatively easily.
Also, in the improved microphone of the invention, the intermediate connector and the another intermediate connector are disposed at the same position along the axis of the cylindrical housing. This has the following effects.
It is possible to interconnect the microphone unit, the cylindrical housing, and the outer cylinder to the ground potential with the shortest distance without a detour. This enables to securely decrease a high-frequency signal, (which contains a modulated signal giving an interference sound to the microphone) which occurs on the microphone unit, the cylindrical housing or the outer cylinder, to the ground potential.
Also, in the improved microphone of the invention, the further intermediate connector is disposed at. such a position in the microphone that is subject to cavity resonance. This has the following effects. A high-frequency signal caused by cavity resonance can be securely decreased to the ground potential. It should be noted that cavity resonance referred to the above-mentioned aspects is supposed to have a frequency from a few tens of mega-hertz to a few giga-hertz.
In addition to the above-mentioned features, preferably the microphone of the invention further includes a supporting member for supporting the microphone unit in the cylindrical housing while blocking mechanical vibrations. This has the following effects.
Although the microphone having such a supporting member can prevent the occurrence of an interference sound caused by the mechanical vibrations occurring at the cylindrical housing, it is difficult construction-wise to electrically interconnect the microphone unit and the cylindrical housing via the supporting member. To guard against this, the supporting member can be provided together with the intermediate connector to thereby achieve supporting and fixing, of the microphone unit in the cylindrical housing and electrical interconnection therebetween, thus preventing the interference sound from occurring.
Also, preferably the microphone of the invention further includes another supporting member for supporting the cylindrical housing in the outer cylinder while blocking mechanical vibrations. This has the following effects.
Although the microphone having such a supporting member can prevent the occurrence of an interference sound caused by mechanical vibrations occurring at the outer cylinder, it is difficult construction-wise to electrically interconnect the microphone unit and the outer cylinder via another supporting member. To guard against this, the another supporting member can be provided together with another intermediate connector to thereby achieve supporting and fixing of the cylindrical housing in the outer cylinder and electrical interconnection between the microphone unit and the outer cylinder, thus preventing the interference sound from occurring.
Also, in the microphone of the invention, preferably the another intermediate connector is uniformly disposed at the gap between the cylindrical housing and the outer cylinder. This has the following effects.
A path for connecting the cylindrical housing and the outer cylinder to the ground potential with essentially the shortest distance without a detour can be naturally formed by the another intermediate connector uniformly disposed at the gap. This enables to securely decrease to the ground potential a high-frequency signal (which contains a modulated signal giving an interference sound to the microphone) occurring at the microphone unit, the cylindrical housing, or the outer cylinder.
Also, preferably the microphone of the invention includes a lid made of a conductor for sealing an end of the outer cylinder as electrically connected thereto and a microphone cable passing through the lid from an inside to an outside of the outer cylinder to thereby lead an output signal of the microphone to the outside in order to electrically interconnect a shield layer of the microphone cable and the lid. This has the following effects.
The cylindrical housing can be electrically connected through the lid to the shield layer of the microphone cable to thereby connect the outer cylinder to the ground potential easily and with the shortest distance.